Development of computer-controlledmachinery for the making up of garments

R. Vitols, M.Tech., Ph.D., C.Eng., F.I.Mech.E., F.R.S.A., B.J.M. Murphy,M.A., C.Eng., M.I.Mech.E., Prof. G.R. Wray, F.Eng., B.Sc, M.Sc.Tech.,Ph.D., D.Sc, C.Eng., F.I.Mech.E., C.Text., F.T.I., A.M.C.S.T., F.R.S.A.,J.E. Baker, B.Sc, F.R.S.A., and T.G. King, B.Sc.(Eng.), M.Des., Ph.D.

Indexing terms: Robotics, Computer applications

Abstract: The automation of making-up operations for the garment industry is discussed in general termstogether with the problems of assembling pliable materials into complex three-dimensional shapes. The paperdescribes work, being undertaken by the Department of Mechanical Engineering at Loughborough Universityof Technology, on the application of sensor-based, intelligent controls for robotic assembly of flexible, knittedcomponents.

1 Introduction

The term 'flexible manufacturing' has a double meaning inthe garment industry. It not only refers to automaticmanufacture of a variety of workpieces, which is vital tothe future well being of this industry; it also refers to theproblem of operating on flexible workpieces, which areliable to alter their shape every time they are moved.

Mechanical engineers at Loughborough University ofTechnology have been working with the textile industryfor nineteen years. A wide range of textile projects havebeen undertaken by members of the Department [1]; theyrange from yarn texturing to garment inspection, and fromthe investigation of individual elements of machines to theinvention and development of complete processes (e.g. the'locstitch' pile fabric machine [2, 3] and developmentsarising from it [4]). Therefore, the Department has a rea-listic and practical approach to the solution of textilemanufacturing problems.

The starting point for work on the automation of themaking-up operations was to accept that the pliableproperties of knitted materials are important during manu-facture, as well as in the finished garment. Progress onautomatic garment assembly will be very limited, unlesscomplex three-dimensional shapes can be produced byflexibly changing the shapes of the component pieces, toenable the matching and joining of edges with differentlengths and curvatures.

The main body panels of fully-fashioned knitted outer-wear garments are knitted on one type of machine,whereas the collars, facings and ribbed waist-bands(collectively known as 'trims') are usually knitted on othertypes of machines. The preferred method of joining thecomponents together is a process known as 'linking', inwhich knitted loops of one component are matched to cor-responding loops of another (see Fig. 1). This is achievedby manually loading particular rows of loops (known asthe 'linking courses') onto a set of grooved points; thesepoints hold the loops in relation to each other, and act asguides for the needle, while the components are sewntogether.

Traditional methods of joining fabric pieces are labourintensive and require high levels of skills, with unrelentingconcentration and good eyesight. Loop-for-loop linking ofknitwear is, perhaps, an extreme example, and knitwear

Paper 3932D (C6, C7), first received 7th February 1985 and in revised form 22ndMarch 1985The authors are with the Department of Mechanical Engineering, LoughboroughUniversity of Technology, Loughborough, Leicestershire LEU 3TV, UnitedKingdom

manufacturers in Leicestershire have encouraged theauthors to find ways of automating such operations.

linking needle'

linking thread grooved points

linking courses

Fig. 1 Linking with a single chain stitchAt point a the looper retains the thread loop so that the needle can pass through thetwo course loops and the thread loop to form a chain stitch. Particular rows ofloops (the linking courses) have been loaded onto the points; if any loop from one ofthe linking courses is not loaded correctly, the resulting fault will spread through thefabric as further loops are pulled undone.

2 Automatic control of machines

2.1 General considerationsImportant criteria for deciding on any machine conceptare

(i) cost: the capital cost of the equipment and also therunning cost, including operators and their overheads

(ii) flexibility: the ability to accept variations in work-pieces

(iii) speed: the overall output of the system(iv) availability: whether the necessary techniques and

equipment have reached a suitable stage of development.

These criteria must be applied stringently when consider-ing automation in the garment industry because

(a) material changes are frequent(b) yarn qualities are inconsistent(c) production runs are often short(d) size ranges are large and ill defined(e) small operating plants are common(/) extreme pressures of fashion are rapid and often

illogical.

Various systems for achieving automatic control ofmachines are discussed in the following text. Fig. 2 is aqualitative indication of how they compare when relatedto the criteria just listed.

2.1.1 Rigid sequence: Such a system may be controlledby cams or limit switches; the changes required to alter thesequencing will often involve skilled fitters and may keepthe machine off the production line for long periods.Therefore the system rates badly for flexibility. On the

178 IEE PROCEEDINGS, Vol. 132, Pt. D, No. 4, JULY 1985

other hand, it is likely to be relatively fast as well as beingcheap to buy and run, because it involves known tech-nology. These important advantages tend to diminish in

cost

availability

poor

Fig. 2 Comparison of control systems

the move away from rigid automation. The fact thatmanufacturers are prepared to accept this loss shows howimportant flexibility is to them.

2.1.2 Preset sequence: The use of controllers of variouskinds can permit changes to be ma"de in a much shortertime than in a rigid mechanical system. This will improvethe flexibility considerably, but the cost and speed will beaffected adversely, depending on the extent to whichspecial motor-driven movements or adjustments are usedin place of preset cams and switches.

2.1.3 Operator/machine interaction: Typical examplesare computer-controlled patterning on a knitting machineand nesting of shapes for cutting. The cost is high and thespeed is low for online operation. Once the sequence hasbeen established and the operator is satisfied, it may bepossible to switch over to 'preset sequence' operation; thiscombined approach increases the speed of operation, butthe extra hardware for interacting with the operator is notfully utilised.

2.1.4 Intelligent robotic systems: Computers can begiven sufficient knowledge to make decisions fast enoughto control machines during their operation. Hence a differ-ent range of flexibility is possible, such as the ability to

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respond to detailed differences in workpieces as well as tooverall style changes. The speed and cost are likely to becomparable with the previously mentioned systems andthe technology can be developed with existing hardware.

2.1.5 Expert robotic systems: This heading is used tocover the range of computer developments which willincrease the flexibility of machine control in the future [5,6]; at present, though, they are either too costly or tooslow and are not readily available as attractive possibilitiesfor immediate use in garment manufacture.

The last two categories are examples of flexible robotics,in which the systems take account of variations in the realworld, rather than relying on a predetermined sequence ofoperations to achieve the desired results.

2.2 Application to knitwearThe systems in Sections 2.1.1-2.1.5 are valuable, separatelyor in combination, but the old adage 'horses for courses'must be applied in order to achieve an optimum solutionto a particular problem.

This approach was used by the Loughborough teamwhen they developed machines for loading ribs onto maga-zines for feeding fully fashioned knitting machines. Thisdevelopment (known as the Loughborough ART process)permitted knitting and automatic loading of body or sleeveribs in a series of preprogrammed operating cycles bymeans of a bolt-on attachment to a vee-bed knittingmachine, sequenced by a programmable linear controller[7, 8]. The resulting machine is now being made and mar-keted by a Leicestershire knitting machine manufacturer(Jordan Lovatt and Jones Ltd.), under licence from Corahpic, who financed much of the original research.

3 Toe closing of socks and trim attaching

3.1 Preliminary researchCurrent research into robotic methods for toe closing andtrim attaching, using the 'intelligent control' possibilities ofcomputers, is at a much earlier stage of development thanthe ART process. The work is concerned with knitted com-ponents having loops which cannot be retained on rigidcarriers between knitting and linking; therefore anotherway must be found to relocate the loops, after they havebeen removed from the needles on which they wereknitted. A control system is required which makes use ofthe flexibility of the computer and its ability to make deci-sions.

Research studies are being made into two operations:these are the toe linking of socks and the linking of collarsand stoles to outerwear. Although they may seem to bevery different operations, both processes require machineswhich are able to:

(a) present the fabric pieces to be worked on(b) sense the pieces and recognise important areas and

shapes(c) position the pieces with appropriate manipulators(d) interface with, or include, mechanisms to perform the

required operations(e) unload the worked-on fabric pieces in a convenient

manner.

The resulting machines would be sophisticated, requiringthe solution of a wide range of new problems.

It was decided that sensing of the linking course (seeFigs. 1, 3 and 4) would be crucial to the progress of thisresearch, with likely applications in areas other thanlinking. Unless the recognition of particular loops and the

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calculation of the positions of their centres could beachieved reliably and quickly without large computing

Fig. 3 Photograph of knitted fabric made with synthetic yarn with 16needles/2.54 cm—full size

directionof knitting

Fig. 4 Large-scale diagram of the fabric+ centre of a loop which is to be selectedO 'inverted' loop which must not be selected

capacity, the project would not be practicable; by contrastall the other problems, although very complex, appearedto be soluble by traditional engineering techniques. There-fore it was decided that the scanning, recognition andcentreline calculation of particular courses of loops wouldbe the priority area of investigation.

A wide variety of sensing methods was investigated; thecriteria used for choosing a system were:

(a) it must use a property which is, or can be, includedin the fabric without serious problems; it must not affectthe customer acceptability of the product, add to the costor cause problems in manufacture

(b) it must be reliable and hence not deteriorate with use(for example, 99.5% reliability on a sock knitted on 200needles would, on average, miss one loop per linking oper-ation which would be unacceptable to the garmentindustry)

(c) it must have a sensing head which will not impedethe manipulating mechanisms; this means that the headmust be small or able to operate at a distance

(d) it must be able to transfer information rapidly andreliably to the manipulator control system

(e) it must not be so expensive or complicated as to beinappropriate for the final product

(/) in addition, it must be able to work on fabrics in theflat or in the round and be able to identify critical featureswithout causing disturbance or damage to the fabric norrelying on measurement from an uneven edge.

With these criteria in mind, vision seemed an obviouschoice [11, 12]. However, some investigations weredirected towards the use of touch, which contributes sig-nificantly to the ability of operators to locate loops manu-ally at surprisingly high speeds. Consideration was givento equipping manipulators with appropriate touch sensors,but this was not pursued, because of the likelihood of wearand speed problems [13]. In any case, it was foreseen thatvision would be required to obtain some of the necessary

information; therefore it was decided to test whether visionalone would be sufficient.

Consideration was also given to including special yarnsor yarns with special treatments, for detection by electricalor other means, but this appeared to offer no advantagesover straightforward optical detection; it would be unde-sirable to use a yarn that made knitting more difficult.However, the task of the vision system could be madesimpler by knitting the first waste course with a yarn of adifferent appearance.

3.2 Sensing and recognition of loopsA research rig has been built which is capable of scanninga piece of fabric in a manner that meets the requirements.It uses a Fairchild 'charge coupled device' (CCD111),which has a line of 256 closely packed sensing elements,each of which is 17 microns long by 13 microns wide [13].This 256 element sensor, complete with a driver board, canbe purchased at low cost.

The initial research has used an Apple II micro-computer with a system clock which runs at 1.023 MHz. Aspecial interface board was made which has four functions:

(i) It transforms the microcomputer system clock toprovide a doubled frequency (2.046 MHz) as the masterclock for the CCD driver board, to transport the videodata from the sensor to the outputs

(ii) It thresholds the data, using a high-speed compara-tor and an adjustable reference voltage, to convert thevideo signal into binary form

(iii) It collects the binary data into 8 bit words, bymeans of shift registers and latches, so that the data can betransferred to the 8 bit microcomputer in the form ofbytes. The time to shift and latch the vision data from thedriver board can be matched precisely by the time to readand store the data into memory, because the devices sharethe same basic clock signal (as described in (i))

(iv) It performs a 'handshake' function between themicrocomputer and the sensor. The signal from the sensordepends upon both the intensity and the duration of thelight it receives. Consistent results are most likely if thesensor runs continuously, otherwise the size of the signalwill depend upon the time that has elapsed since the pre-vious run. A series of counters provides a regularexposure-synchronising pulse to initiate the transportregisters. There is a specific delay between sending thispulse and the receipt of data at the interface board; thistime is used to ensure that the microcomputer startsrunning through the program that reads the input port insynchronism with the arrival of the first byte of data.

A special-purpose single-board computer, using a 6502microprocessor, has been built to perform the functions ofthe Apple and the interface board; such a device would beused in a commercial machine, but it is convenient to con-tinue to use the additional facilities offered by the Apple inthe research stages.

The information from one scan of the sensor is read bythe microcomputer in a quarter of a millisecond. This datacan be processed by a series of simple programs, workingon intelligent-knowledge-based-system lines, to performthe calculations necessary to follow a line of loops and findparticular loop centres in half a millisecond. With the pro-posed mechanical arrangements, the computer can processsensor information from scans viewed at intervals ofbetween 0.04 and 0.08 mm.

Fig. 3 shows an example of a knitted fabric which hasbeen processed by the rig. Fig. 4 is an enlarged diagram-matic representation of a knitted structure and indicates

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which loops must be detected. Fig. 5 is a print out of theinformation received by the computer when part of the

Fig. 5 Print out from sequential scans of the fabric+ approximate centres of selected loops

fabric of Fig. 3 is scanned; this print out shows the irregu-larity of the pattern, the variations in size of the loops andthe fuzziness of the edges that the system must be capableof accepting.

3.3 Toe closing of socksWork was concentrated initially on the toe linking of socksbecause of the firm encouragement of a local sock manu-facturer. So far, only a conceptual study, economic analysisand some preliminary design work have been undertakenon this proposal.

Socks are commonly knitted in a continuous string, sothat the open toe of one sock is attached to the top of thenext sock by a special yarn and some knitted rows whichwill be removed later. It was intended that a machineshould be designed to link toes of socks knitted in thismanner. An operator would load a string of socks onto amandrel; then the machine would turn the socks inside outand feed the string along the mandrel, while a sensingdevice would search for a corner of the toe pouch and indi-cate the approximate position for the start of the linkingcourse (i.e. the row of loops along which linking will takeplace). Another sensing device would scan along thelinking course, recognise the loops which would need to belinked, calculate the positions of the loop centres andcontrol the engagement of points with the loops. Withpoints inserted in all the linking loops, the sock would beseparated so that the machine could index the sock, part ofthe mandrel and the point carrying mechanism through180 degrees, to bring the scanned sock to the linking posi-tion and, at the same time, index another set of linkingpoints to the scanning position. At the linking position thepoints would be matched and aligned in pairs, and the toewould be closed. Then this sock would be unloaded andthe next sock indexed into position.

Recently the emphasis of this work has changed. Theauthors realised that machinery for toe-linking sockswould have special features which might not suit othergarment assembly operations. Therefore other aspects werestudied which would have a wider and more immediateapplication. Hence it has been decided to concentrate onthe linking of collars and similar trims to outerwear gar-ments (with the co-operation of Corah pic).

3.4 Collar and trim attachingThe basic sensing system for finding loop centres will bemuch the same as before, but some of the programs whichmake the decisions will be different, although working tothe same principles.

The machine concept would be substantially different.Collars or trims would be knitted as a continuous lengthin the conventional manner, whereby each one is joined tothe next by rows of draw thread; this thread, as its nameimplies, is withdrawn to separate the bulk supply into indi-vidual trims at an appropriate stage of manufacture. Amachine of a new design would feed these collars forward,then monitor and approximately position each linkingcourse, which is normally knitted with slightly less tensionon the yarn than the remainder of the fabric. The linkingcourse would then be scanned, and transfer points insertedinto the appropriate loops. After removal of the drawthread, a separate mechanism would transfer the collaronto a magazine bar which would be capable of acceptinga large number of collars for subsequent linking to thebody of the garment.

The functions under computer control would includethe following:

(a) the initial feeding of trims(b) sensing and recognising the linking course(c) controlling the engagement of points(d) catering for widths of trims which vary with styles(e) the loading of magazine bars(/) interacting with the operator for changes of bulk

supply.

An economic study of the proposed system, using project-ed figures for machine costs and outputs, is favourable, notonly in comparison with manual linking but also whencompared to the lower quality, approximate-linkingsystems.

4 Conclusions

Sensing of workpieces, combined with real-time control ofmanipulating devices, is a vital stage in progress towardsautomation of most manufacturing processes, but currentrobotic systems are too slow or expensive to be applicableto the making up of knitted garments. A new roboticsystem is required for knitwear which is capable of detect-ing and recognising the large number of loops to be joined,and of controlling a similar number of manipulators tobring these loops into correct relationships; also, it mustbe able to perform these functions within an acceptabletime and for a reasonable cost.

The problem is not easy to solve, but the market isthere; a report on 'the state of the art of assembly ofapparel products', prepared for the Commission of theEuropean Economic Community in 1979, stated that '80%of the direct operative work force spends 90% of its timepicking-up, positioning, manipulating and removing oneor more pieces of fabric around a stitch making device'[14]. This assessment related to a work-force of 2.7 millionin the developed countries.

Instead of the pliability of garment fabrics being anunsurmountable obstacle to automation, the authorsbelieve that, in most cases, it must be utilised when joiningcomponent pieces together, otherwise the resultinggarment will not be acceptable. This is obvious to textiletechnologists, but it is not always as clear to robotics engi-neers who usually work with rigid materials. The authorshave gained substantial research and design experience inthe knitwear industry, and they look forward enthusiasti-

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cally to facing new and unusual challenges in progresstowards the wider automation of assembly by means offlexible robotics.

5 Acknowledgments

The authors wish to acknowledge the overall contributionsmade by their colleagues; also the support and assistancegiven to them over a number of years by Corah pic, inparticular, as well as by several other textile manufacturingand machinery companies.

Part of the research referred to in this paper has beenfunded by the UK Science and Engineering ResearchCouncil; the most recent work is under the auspices of thatCouncil's 'Robotics Initiative' and this support is gratefullyacknowledged.

6 References

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2 WRAY, G.R., WARD, G.F., and VITOLS, R.: 'Studies in modernfabrics'. The Textile Institute, Manchester, 1970, pp. 30-39

3 WRAY, G.R.: 'The application of mechanism theory to a textilemachinery innovation', Proc. l.Mech.E., 1976, 190, pp. 367-378

4 VITOLS, R., VINE, J.E., WALKINSHAW, S., and WRAY, G.R.:'Fabric revolution'. The Textile Institute, Manchester, 1981

5 JOHNSTON, R.: 'How close are we to thinking machines?', Com-puter Talk, 14th November 1983, pp. 15-16

6 WINSTON, P.H.: 'Artificial intelligence' (Addison-Wesley, 1979), p.237

7 WRAY, G.R., and VITOLS, R.: in HAPPEY, F. (Ed.): 'Contempo-rary textile engineering'. Textile Institute, London, 1983, p. 404

8 Anon: Knitting International, 1982, 89, (1057), p. 969 Corah pic E.P. 10982. (2nd Aug. 1978)

10 DAVEY, P.G.: 'Robots with common sense! The research scenetoday', J. Royal Soc. Arts, 1983, CXXXI, (5327), pp. 671-685

11 CLARK, I.: 'Image scanners: the eyes of tomorrow's machines',Sensor Rev., 1981, 1, (1), pp. 20-24

12 HARMON, L.D.: 'A sense of touch begins to gather momentum',ibid., 1981

13 TROWBRIDGE, M.: 'Image sensors in system design', Eng. Mater. &Des., 1981,25, pp. 22-23

14 KURT SALMON ASSOCIATES: 'The 1980s: the decade for tech-nology?'. Report for the Commission of the European EconomicCommunity (December 1979), pp. 1-5

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